It is well known to use bolts to fasten assembly components together. Typically, bolt fastening requires bolt holes in each of the connected components that are aligned so the bolt may be inserted there through. Additional complexity may be introduced where multiple bolts are used to fasten the components. The bolt holes through each component must be arranged in corresponding patterns that align during assembly so that all bolts may be inserted though the bolt holes. Consequently, the relatively basic use of bolts to fasten assembly components may become more complex and require greater precision in particular implementations.
In one such implementation in gas turbine engines, fan structural guide vanes are used to provide air flow control between a fan containment case and forward mounts to the front center body and core. Connection of the guide vanes requires tightly controlled bolt holes to effectively transfer shear loads from the guide vanes to the fan case. It has been observed that holding small clearances within a pattern of bolts requiring precise spacing effectively distributes shear among all fasteners within the pattern. It is difficult on a large assembly such as a fan case, where multiple materials make up a bolt stack, to control hole sizes and positional tolerance to levels required to align the fan case bolt holes to the corresponding bolt holes of the guide vanes to provide the designed shear load sharing. It is undesirable to line drill holes in the fan case at assembly due to part replacement requirements. Moreover, in some implementations, bushings are inserted through the bolt holes of the fan case and provide the primary bearing surfaces for shear stresses that are distributed to the fan case. Where the fan case is fabricated from metal, the bushings may be press fit into the bolt holes without damaging the fan case. As the design of fan cases transitions to the use of composite materials, press fitting of bushings into the bolt holes through the composite material wall can cause local cracking that can compromise the integrity of the fan case.
In view of the foregoing, a need exists for an improved arrangement in certain assemblies for tightly controlled bolt hole installation, and for methods for maintaining the tight control of the bolt holes during construction of the assemblies.